It is well known that overall fuel efficiency in a multiple-cylinder internal combustion engine can be increased by selective deactivation of one or more of the engine valves, especially the intake valves, under certain engine load conditions. For cam-in-block engines, a known approach to providing selective deactivation is to equip the hydraulic valve lifters for those valve trains with means whereby the lifters may be rendered incapable of transferring the cyclic motion of the engine cam into reciprocal motion of the associated valves. For an overhead-cam engine, a known approach is to equip the hydraulic lash adjusters for those valve trains with means whereby the rocker arm may be rendered incapable of transferring the motion of engine the cams into reciprocal motion of the associated valves.
Typically, a DHLA includes, in addition to the conventional hydraulic lash elimination means, a concentric inner pin housing and outer HLA body which are mechanically responsive to the force of the rocker arm as exerted by the cam lobe, and which may be selectively latched and unlatched hydromechanically to each other, typically by the selective engagement of pressurized engine oil on locking pins.
An important consideration in a DHLA is the amount of internal mechanical lash deliberately incorporated into the DHLA. In prior art DHLAs, a transverse bore in the pin housing contains the two opposed locking pins which are urged outwards of the pin housing by a pin-locking spring disposed in compression therebetween to engage a circumferential groove including a locking surface in the inner wall of the HLA body whereby the HLA body and the pin housing are locked together to produce reciprocal motion of a rocker arm disposed on the DHLA. When valve deactivation is desired, the pins are withdrawn from the DHLA body by application of hydraulic fluid such as engine oil to the outer ends of the pins at pressure sufficient to overcome the force of the pin-locking spring.
Prior art DHVLs, such as shown in U.S. Pat. No. 6,578,535, typically are assembled from a top end of the DHVL body (which is closed at its bottom end) by insertion of components through the open top end and securing the components with one or more retaining rings and the like, fitting into an annular groove formed in the inner wall of the DHVL body below the open end thereof. The rings also serve to set internal mechanical lash in the DHVL by the selection of rings of appropriate thickness during assembly of the DHVL. The rings act as a mechanical stop to limit the outward motion of the pin housing prior to engagement and disengagement of the locking pins. Preferably, the lash rings permit the pin housing to travel to a position wherein the locking pins can clear the bottom surface, or ledge, of the locking feature in the DHVL body by a small amount, typically about 0.005 inches or less. Excess internal mechanical lash results in clatter and wear of the DHVL during engine operation, and can have an adverse effect on the lift characteristics of the associated valve. Thus, controlling the axial position of the underside of the retaining rings with respect to the ledge of the locking feature is of critical importance.
Typically, because of variation in manufacturing tolerances of the body, pin housing, and pins, the correct lash is obtained only by iterative trial and measurement using rings of differing thickness. However, setting the lash in this fashion is difficult, requiring repeated assembly and disassembly of the pin housing from the DHVL body because accessing the lash-setting retaining snap rings to remove the pin housing once installed is difficult and complicated.
Further, in cases where the wall of the DHVL body is thin because of packaging constraints, the presence of an inner-wall annular groove for the retaining rings near the open end of the DHVL body structurally weakens the wall of the body.
Referring to U.S. Pat. No. 6,513,470, a spring seat is shown for an external lost motion (LM) spring in a DHVL, wherein the spring seat also functions as a variable-thickness shim for setting the internal mechanical lash in each valve deactivation assembly. The spring seat is held in place by the LM spring that is captured by a spring tower. The spring seat rests on the outer end of the lifter body and also includes a cylindrical portion that extends into the lifter bore to engage the pin housing therein, the cylindrical portion being selectively varied to control mechanical lash. Thus, the seat serves to control mechanical lash without a requirement for a retaining groove in the inner wall of the lifter bore.
This latter approach for setting lash is not adaptable to current DHLAs since, in prior art DHLAs, the LM spring is internal to the assembly, and thus there is no spring seat requirement at the outer end of the body.
What is needed in the art is an improved DHLA wherein components are easily assembled, wherein mechanical lash is easily set, and wherein an annular groove for locking a retaining ring is obviated.
It is a principal object of the present invention to reduce the cost and complexity of an improved DHLA, to improve the ease and reliability of assembly thereof, and to increase the operating reliability thereof.